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A conductor whose purpose is to emit and/or receive electromagnetic waves using the bulk oscillations of electric charges within the conductor. The conduction electrons in antennas are free to move throughout the conductor. The electrons form a bulk…

The subfield of computer science concerned with understanding the nature of intelligence and constructing computer systems capable of intelligent behavior. Many activities, such as perception, learning, planning, natural language, and understanding,…

A kind of mathematics whose variables can only be True or False. A variable is called Boolean if it can only hold two possible values: True or False. The value True can be represented by the number one and False by zero. For example, if A is a…

Cameras in mobile phones or smartphones that can capture images and videos.The cellphone, the world’s favorite must-have gadget, has been with us for nearly a half-century, while experiencing continuous and often phenomenal improvements. Much of the…

A branch of computer science that deals with the theory and techniques of computer-generated images. Computers produce images by analyzing a collection of dots, or pixels (picture elements). Computer graphics is used to enhance the transfer and…

A radar system used to measure the relative velocity of targets and their position. The operation of these systems is based on the fact that the Doppler frequency shift in the target echo is proportional to the radial component of target velocity.…

A mathematical system that details the properties and relationships of spatial objects such as points, lines, shapes, and planes. Euclidean geometry is also known as flat geometry or planar geometry, because planes in Euclidean geometry have the…

An interdisciplinary science area that is concerned with modeling aspects of natural evolution in order to solve real-world problems of optimization. Living organisms, as well as those that are long extinct, demonstrate optimized complex behavior at…

The inverse function of an exponential function in mathematics. Stated less technically, a logarithm is the opposite of an exponent. Logarithms are used to solve equations in which the variable is an exponent. Historically, tables of logarithms…

A branch of mathematics involving numerical measures of how likely it is that a particular event will occur. A probability is a number between 0 and 1. An event that will never occur has a probability of zero, and an event that is certain to occur…

Computation that encodes data in quantum objects to later process that data using operations based on the concepts and principles of quantum mechanics. Quantum objects used in quantum computation include the nuclei of atoms, ions in a crystal,…

In medicine and health sciences, a value expected for an individual whose state of health is known and well described, and the interval of values broadly expected for a population, respectively. Results of clinical laboratory tests and other…

The evolving internet technologies for content sharing and collaborating among communities of online users. Since the advent of the Web 2.0—the more dynamic and interactive second generation of the World Wide Web—the term social media has become…

The field of knowledge concerned with collecting, analyzing, and presenting data. Statistical methods are regularly used by researchers in the physical, biological, and social sciences, as well as engineers, business managers, government officials…

The theory of circuits made up of ideal digital devices. Included in switching theory are the theories of circuits and networks for telephone switching, digital computing, digital control, and data processing. Computer Electrical circuit Electronic…

A management technology involving the interactions of science, an organization, and its environment as well as the information and knowledge that support each. The purpose of systems engineering is to support organizations that desire improved…

A process of making physical objects directly from digital models, usually layer by layer; also known as additive manufacturing (AM). 3D printing has been hailed by many as the technology that will revolutionize how we live. As information…

The study of systems consisting of arbitrary sets of elements of unspecified type, together with certain operations satisfying prescribed lists of axioms. Abstract algebra has been developed since the mid-1920s and has become a basic idiom of…

A statistical technique that partitions the total variation in experimental data into components assignable to specific sources. Analysis of variance is applicable to data for which (1) effects of sources are additive, (2) uncontrolled or…

A discipline that combines biology, mathematics, and computer science to acquire, store, analyze, and disseminate complex biological data. The term bioinformatics was coined by Paulien Hogeweg and Ben Hesper in the early 1970s to describe the "the…

In its simplest form, a vector is a directed line segment. Physical quantities, such as velocity, acceleration, force, and displacement, are vector quantities, or simply vectors, because they can be represented by directed line segments. The algebra…

A natural and extremely useful extension of the familiar real numbers. They can be introduced formally as follows. Consider the two-dimensional real vector space consisting of all ordered pairs (a1, a2) of real numbers. Geometrically this space can…

A device that receives, processes, and presents information. The two basic types of computers are analog and digital. Although generally not regarded as such, the most prevalent computer is the simple mechanical analog computer, in which gears,…

Any device connected internally or externally to a computer and used in the transfer of data to or from a computer. A personal computer (PC) processes information. Data (unprocessed information) must get into the computer, and the processed…

Designing and writing a detailed sequence of operating instructions for a particular problem to be run on a computer; also known as programming. A computer is able to perform useful tasks only by executing computer programs. A programming language…

The process of protecting against threats to computing systems. A threat is an event that can cause harm to computers, data or programs, or computations (Fig. 1). A failure of computer security occurs because of a vulnerability or weakness in a…

The hardware components, both internal and external, of a computer used to read (retrieve) or write (save) digital data. The ability to read and write data is an essential function of a computer and of the so-called von Neumann architecture…

A program or script that is loaded and executed on a computer without the knowledge of the user. A typical computer virus is a very small program, several kilobytes or less in size, constructed in a matter of hours or days. When executed, the virus…

The technology concerned with computational understanding and use of the information present in visual images. In part, computer vision is analogous to the transformation of visual sensation into visual perception in biological vision. For this…

A digital equivalent of paper banknotes. Just like paper banknotes, cryptocurrencies allow users to maintain privacy in digital commercial transactions while ensuring that value is transferred from one party to the other. Cryptocurrencies achieve…

A curve traced in the plane by a point on a circle that rolls, without slipping, on a line. If the line is the x axis of a rectangular coordinate system, at whose origin O the moving point P touches the axis, parametric equations of the cycloid are…

A branch of mathematics that deals with intrinsic properties of curves and surfaces in three-dimensional Euclidean space. The intrinsic properties are those which are independent of the geometrical object's orientation or location in space. The…

The computer manipulation of visual data to solve a problem. The problems under consideration are of two primary types: (1) those that require a computer to act on the resultant images, and (2) those that provide images for human interpretation. The…

In arithmetic and algebra, the process of finding one of two factors of a number (or polynomial) when their product and one of the factors are given. The symbol ÷ now used mostly in elementary English and American arithmetics to denote division…

Programmable computers integrated with electrically powered machines that perform household chores. Domestic robots, also known as home or service robots, are essentially programmable computers integrated with electrically powered machines that…

The number e usually defined as the limit approached by the expression as n approaches infinity. If the given expression is expanded by the binomial theorem, and if one uses the theorem that the limit of the quotient of two polynomials of equal…

The manner in which electromagnetic waves travel forward along a path. Electromagnetic waves consist of quantized, traveling, self-sustained, electromagnetic field fluctuations. The high speed of electromagnetic waves makes them useful in…

A System that locates suitably equipped users by means of measurements made by electronic sensors. Typical measurements include distance or bearing from a vehicle to a known point, or direct determination of the present position of the vehicle in a…

A method of quantitative multivariate analysis with the goal of representing the interrelationships among a set of continuously measured variables (usually represented by their intercorrelations) by a number of underlying, linearly independent…

In algebra, the term "field" is used to designate an algebraic system or structure containing at least two elements and having two binary rules of composition: addition and multiplication (that is, if a and b are any two elements of the field, then…

A branch of mathematics concerned with the properties of space, including points, lines, curves, planes and surfaces in space, and figures bounded by them. Multiple kinds of geometry exist, dealing with everyday concepts such as lengths, angles, and…

The responsible use of computer and related resources with the objective of curbing the negative effects that the increasing use of computers and their associated technologies have on the Earth's limited natural resources. Green computing is part of…

An interdisciplinary field focused on the interactions between human users and computer systems, including the user interface and the underlying processes that produce the interactions. The contributing disciplines include computer science,…

The field of engineering involving computer-based hardware and software systems, and communication systems, to enable the acquisition, representation, storage, transmission, and use of information. Information technology (IT) is critically dependent…

Intentional generation of interfering signals in the electromagnetic spectrum by powerful transmitters as a countermeasure intended to block a communication, radar, or infrared system or to impair its effectiveness appreciably. Radio broadcasts or…

A topological group with only countably many connected components whose identity component is open and is an analytic group. An analytic group or connected Lie group is a topological group with the additional structure of a smooth manifold such that…

That branch of mathematics which deals with solutions of systems of linear equations and the related geometric notions of vector spaces and linear transformations. It is fundamental in the theory of the calculus of functions of several variables and…

A branch of artificial intelligence (AI) based on the notion that machines (software applications) can learn from examples and can teach themselves how to solve specific problems without being programmed manually. Recent successes in artificial…

The application of mathematics to biological systems. Just as physics underlies many engineering technologies, biology serves as a foundation for such disciplines as medicine, agriculture, animal husbandry, and environmental sciences, in which…

The study of the patterns and relationships that arise between abstract concepts. Though studied purely for its own sake, mathematics is the language with which all rigorous science is discussed. As the German-born U.S. theoretical physicist Albert…

Computer software that is licensed by the copyright holder, granting the rights to examine, change, and distribute it to anyone and for any purpose as long as the original copyright statement in any redistributed software is preserved. The…

A ratio comparison of two quantities expressed by using 100 equal parts, or hundredths; symbolized %. There are three major uses of percent: part of a whole, rate, and comparison of any two quantities. Part of a whole The basic idea of percent is as…

The notation used to communicate instructions to a computer. A computer executes a sequence of instructions (a program) in order to perform some task. The set of instructions and the order in which they have to be performed is known as an algorithm.…

The means by which radio waves move from one place to another. A radio wave is an electromagnetic wave that has a frequency within the radio-frequency spectrum, from 3 kHz (3000 Hz, where Hz is the symbol for hertz, a unit of frequency defined as…

A set of instructions that causes a computer to perform one or more tasks. The set of instructions is often called a program or, if the set is particularly large and complex, a system. Computers cannot do any useful work without instructions from…

The production of software through a progression of disciplined and controlled steps. As the need for complex, real-time, and life-critical software proliferates, there is a demand for an effective software development process that guarantees the…

A device that automatically measures the angular separation of stellar observations with respect to a reference platform. It is also referred to as an astrotracker.By utilizing the star tracker in conjunction with a precise time reference…

A hissing, crackling, or other sudden sharp noise that tends to interfere with the reception, utilization, or enjoyment of desired signals or sounds. Perhaps the commonest form of static is that heard in ordinary broadcast receivers during…

The transmission of stereophonic audio signals over broadcast radio systems, including terrestrial analog amplitude-modulation (AM), frequency-modulation (FM) systems, and digital radio systems (terrestrial and satellite). Stereophonic…

The assertion that under certain light restrictions the surface integral of (∇ × ℑ) · ν over a surface patch S is equal to the line integral of ℑ · τ taken around C, the boundary curve of S, provided the sense of transcription of C is right-handed…

A cable laid on the ocean floor to transmit signals. The challenge for submarine cables has been to convey signals long distances under water where there is no opportunity for easy access at intervening points. In the 1850s these were direct-current…

One of the four fundamental operations of arithmetic and algebra. The first printed use of the symbol − to denote subtraction is in Johann Widman's Behennde und hüpsche Rechnung, Leipzig, 1489. Subtraction is often regarded as an operation inverse…

A two-dimensional geometric figure (a collection of points) in three-dimensional space. The simplest example is a plane—a flat surface. Some other common surfaces are spheres, cylinders, and cones, the names of which are also used to describe the…

A member of the rho-theta family of air navigation systems which define an aircraft's position by its distance and bearing to a single beacon. Such systems inherently answer the navigator's questions of “in what direction” and “how far,” without…

A term describing a relationship of two figures (usually of the same dimension) in the neighborhood of a common point. The figures are tangent at a point P if they touch at P but do not intersect in a sufficiently small neighborhood of P. To be more…

In a broad sense, teleconferencing encompasses the various ways and means by which people communicate with one another over some distance. In a narrow sense, a teleconference is a two-way, interactive meeting among individuals or relatively small…

A method of communication employing electrical signaling impulses produced and received manually or by machines. Telegraph signals are transmitted over open wire or cable land lines, submarine cables, or radio. Telegraphy as a communication…

The branch of engineering, also called telemetry, which is concerned with collection of measurement data at a distant or inconvenient location, and display of the data at a convenient location. One example of a complex telemetering system is used to…

A handheld device that permits communication over a network between persons who are in different locations. A traditional telephone instrument, also called a set, contains a transmitter for converting the acoustic signals of a person's voice to…

The technology of providing many types of communications services via networks that transmit voice, data, image facsimile, and video by using both analog and digital encoding formats. Component sectors and core technologies Telephone services…

Construction of the physical components of the telephone system from the central office to the end user. The telephone system can be roughly divided into three major components: outside plant, switching equipment, and interoffice facilities. The…

The electrical transmission and reception of transient visual images. Like motion pictures, television consists of a series of successive images which are registered in the brain as a continuous picture because of the persistence of vision. Each…

An electrooptical system used to pick up and convert a visual image or scene into an electrical signal called video. The video may be transmitted by cable or wireless means to a suitable receiver or monitor some distance from the actual scene. It…

Arrangements of communications channels, suitable for transmission of video and accompanying audio signals, which link together groups of television broadcasting stations or closed-circuit television users in different cities so that programs…

The process used to convert a three-dimensional image intensity into a one-dimensional television signal waveform. The image information captured by a television camera conveys color intensity (in terms of red, green, and blue primary colors) at…

The accepted criteria for a television system, including the image aspect ratio, number of lines per frame, type of scanning, original video signal bandwidth, transmission format and bandwidth, reception, demodulation, decoding, and sound system.…

A facility designed for the production of television programs, which may be broadcast live concurrently with the production or recorded for later broadcast. A television studio consists of the studio room, wherein the actual program takes place, and…

The systematic study of tensors which led to an extension and generalization of vectors, begun in 1900 by two Italian mathematicians, G. Ricci and T. Levi-Civita, following G. F. B. Riemann's proposal concerning a generalization of Euclidean…

A proposition arrived at by the methods of logical deduction from a set of basic postulates or axioms accepted as primitive and therefore not subject to deductive proof. So long as a theorem is part of a purely formal system, it is not meaningful to…

The branch of mathematics concerned with finding facts concerning the roots of algebraic equations and finding methods for obtaining them. The most important type of algebraic equation is the polynomial equation in one unknown which is an expression…

The study and application of topological transformation groups. Topological dynamics originated in the late-nineteenth-century investigations of the qualitative behavior of the solutions to the differential equations of classical mechanics by Henri…

The branch of mathematics that studies the qualitative properties of spaces, as opposed to the more delicate and refined geometric or analytic properties. While there are earlier results that belong to the field, the beginning of the subject as a…

A surface obtained by rotating a circle about a line that lies in the plane of the circle but that has no points in common with the circle (see illustration). The equations x = u cos v, y = u sin v, z = [r2 − (u − b)2]1/2, b > r > 0, represent the…

An electronic display that allows a user to interact with a computer system by touching an area or areas on the display. Touch-screen displays have been in use for many years in ATMs, checkout registers, and other applications, but gained mass…

A plane curve for which the length of any tangent between the curve and a fixed line is constant c. If the x axis is the fixed line, its differential equation is Eq. (1). 1 With ψ, the inclination of the tangent, as pa­ram­eter, this yields Eqs.…

The study of triangles and the trigonometric functions. One common use for trigonometry is to measure heights and distances that are awkward or impossible to measure by ordinary means. Surveyors use it to find heights of mountains and distances…

Electronic systems that transmit radio-frequency (RF) energy with either (1) an instantaneous bandwidth of at least 500 MHz, or (2) a 10-dB fractional bandwidth (ratio of the instantaneous bandwidth measured at the –10 dB points to the center…

A term that became part of mathematical language during the development of analytic geometry (no equivalent word is found in the writings of Archimedes and other Greek mathematicians), and which is frequently not defined in modern works, apparently…

A mathematical element used to describe quantities having magnitude and direction. It can be represented by a directed line segment. Many physical quantities, for example, velocity, acceleration, and force, are vectors. Vectors are widely used in…

The second generation of the World Wide Web (WWW), which is more dynamic and interactive than its predecessor, Web 1.0. Although the term Web 2.0 follows the trend to number the new releases or versions of software products, in reality the term is…

A whole number, 0, representing the number of things in a group with no objects. In mathematics, zero (see illustration) is conceptually used both as a number and as a value of a variable. Mathematics A typical depiction of the number "0" as an…

An early mechanical calculator. The abacus likely originated in Babylonia sometime before 1000 BCE. Over the subsequent centuries, it became a commonplace device in many regions of the world. The abacus is still occasionally used as a cognitive…

A discipline that deals generally with the extraction of information from acoustic signals in the presence of noise and uncertainty. Acoustic signal processing has expanded from the improvement of music and speech sounds and a tool to search for oil…

A group of software development methods in which requirements and solutions evolve through collaboration between the developers and the customers. Agile methods have significantly changed the practice of software development since their inception…

A discipline that combines the means to know the location and heading of an aircraft with respect to some map or coordinate system, with guidance which means steering the aircraft along some desired path toward a destination. The construction of the…

The branch of mathematics dealing with the solution of equations. These equations involve unknowns, or variables, along with fixed numbers from a specified system (Fig. 1). The origins of algebra were based on the need to develop equations that…

The study of zero sets of polynomial equations. Examples of zero sets of polynomial equations studied in algebraic geometry are the parabola y − x2 = 0, thought of as sitting in the (x, y)-plane, and the locus of all points (t, t2, t3, t4), which is…

A binary digit. In the computer, electronics, and communications fields, “bit” is generally understood as a shortened form of “binary digit.” In a numerical binary system, a bit is either a 0 or 1. Bits are generally used to indicate situations that…

A system that receives and processes television signals, as well as other digital forms of communications such as those related to high-speed Internet connectivity and cable telephony, from various sources and retransmits these signals through…

An electronic device that performs arithmetic, statistical, or other, more complex processing operations at the step-by-step direction of the user or by execution of a program (a stored sequence of processing operations) selected and initiated by…